MH's ideal coil and voltage question

[tinman]

I would agree.
Good question. If you read that web page it tells you that the induced cemf is proportional to the number of turns in the coil. (you should read the link provided, it does explain everything).

Yes,i read that page some time ago,and reviewed it again after your post with the link to it.]

Quote: The reduction of current flow in a circuit due to induction is called inductive reactance. By taking a closer look at a coil of wire and applying Lenz's law, it can be seen how inductance reduces the flow of current in the circuit. In the image below, the direction of the primary current is shown in red, and the magnetic field generated by the current is shown in blue. The direction of the magnetic field can be determined by taking your right hand and pointing your thumb in the direction of the current. Your fingers will then point in the direction of the magnetic field. It can be seen that the magnetic field from one loop of the wire will cut across the other loops in the coil and this will induce current flow (shown in green) in the circuit. According to Lenz's law, the induced current must flow in the opposite direction of the primary current. The induced current working against the primary current results in a reduction of current flow in the circuit.

It should be noted that the inductive reactance will increase if the number of winds in the coil is increased since the magnetic field from one coil will have more coils to interact with.

This still dose not explain as to where the loss is--why the  CEMF is not equal to the induced EMF.
If the CEMF and EMF were of the same amount,then the current that flows in opposition to that which created it,would be of the same value,and no current would flow.
So where is this loss?
Could it be that some is due to the actual resistance value of the coil,and/or the fact that the outer windings and inner windings do not cut through as many other windings as those in the center of the coil do.
What i mean is,is this loss due to incomplete total flux linkage within the inductor?.

Just on that note.
MH has just said that the CEMF is equal to the EMF that created it.
Your thoughts on this?


Brad

[MileHigh]

Here Brad, let's use the integral equation for a coil that relates the current and the voltage to solve for the question:

i(t) = 1/L integral v(t) dt

Let's just look at the first three seconds.

We know that the voltage is 4 volts and it is unchanging.   We know that the inductance is 5 Henrys.  So let's just punch in the numbers then.

i(t) = 1/5 integral 4 dt

Then you go to the integral web site and you get the solution for the integral.  You were too emotionally exhausted and burnt out so you never went there.

i(t) = 1/5 (4t)

Rearranging and cleaning up:

i = 4/5 * t

i = 0.8t

For t = 3 seconds we get i = 2.4 amperes.

Same story.  If you just got up the learning curve and changed your bad attitude all of the weeks and weeks of agony could have been answered in 90 seconds flat.

[tinman]

PW

My short answer would be "geometry", with regard to flux cutting/coupling...

Ah,just read your post PW,as i just finished posting my last one.
Seems we are on the same page here.

Consider a given length of conductor (wire).  Stretched out straight it has a certain, lowest value of inductance.  Coiled up it has more inductance.  Change the diameter and/or spacing of the coiled turns and the inductance changes.  In any configuration, changing the size and shape of the conductor's cross section also changes the inductance.

Yes,i agree with all this.
So if we could achieve this perfect coupling/flux cutting,then the CEMF should be equal to the EMF that created it. In this case,no current would flow?


Brad

[tinman]

Here Brad, let's use the integral equation for a coil that relates the current and the voltage to solve for the question:

i(t) = 1/L integral v(t) dt

Let's just look at the first three seconds.

We know that the voltage is 4 volts and it is unchanging.   We know that the inductance is 5 Henrys.  So let's just punch in the numbers then.

i(t) = 1/5 integral 4 dt

Then you go to the integral web site and you get the solution for the integral.  You were too emotionally exhausted and burnt out so you never went there.

i(t) = 1/5 (4t)

Rearranging and cleaning up:

i = 4/5 * t

i = 0.8t

For t = 3 seconds we get i = 2.4 amperes.

Same story.  If you just got up the learning curve and changed your bad attitude all of the weeks and weeks of agony could have been answered in 90 seconds flat.

Well that was boring MH,as i have already answered the question using the very formula you just used. Perhaps go back say 200 posts,and have a look.

I think the agony here,is having to keep going over the same stuff an endless amount of times with you.


Brad

[poynt99]

This still dose not explain as to where the loss is--why the  CEMF is not equal to the induced EMF.
If the CEMF and EMF were of the same amount,then the current that flows in opposition to that which created it,would be of the same value,and no current would flow.
So where is this loss?
Could it be that some is due to the actual resistance value of the coil,and/or the fact that the outer windings and inner windings do not cut through as many other windings as those in the center of the coil do.
What i mean is,is this loss due to incomplete total flux linkage within the inductor?.

I think you have the basic concept, yes. Again, the fundamental frequency and the harmonic content influences how the inductor reacts. The higher the inductance, the higher the induced cemf for a given frequency. At some point (either relatively large L or high frequencies) the cemf will equal the applied voltage (or it may be more correct to say the induced current will equal the applied current) and the net resulting current will be minimal.

Just on that note.
MH has just said that the CEMF is equal to the EMF that created it.
Your thoughts on this?

I'll let MH explain that.